Rice (Oryza sativa L.) inflorescence (panicle) architecture is an important agronomic trait for rice breeding. A number of high-yielding japonica rice strains, characterized by an erect panicle (EP) of their architecture, have been released as commercial varieties in China. But no EP-type indica varieties are released so far. Here, we identified two allelic erect-panicle mutants in indica rice, erect panicle2-1 (ep2-1) and erect panicle2-2 (ep2-2), exhibiting the characteristic erect panicle phenotype. Both mutants were derived from spontaneous mutation. We cloned the EP2 gene by way of a map-based cloning strategy, and a transgenic complementation test rescued the phenotype of ep2-1. Anatomical investigations revealed that the ep2 mutants have more vascular bundles and a thicker stem than that of wild-type plants, explaining the panicle erectness phenotype in ep2 mutants. It was shown that EP2 was specifically expressed in the vascular bundles of internodes by GUS staining and RT–PCR. EP2 encodes a novel plant-specific protein, which localizes to the endoplasmic reticulum with unknown biochemical function. In addition, EP2 also regulates other panicle characteristics, such as panicle length and grain size, but grain number per panicle shows little change, indicating that the mutation of the ep2 gene could be applied in EP-type indica rice breeding.
穗型是水稻育種上一個(gè)重要的農(nóng)藝性狀。大量直立穗型粳稻新品系已經(jīng)作為商業(yè)品種在中國得到推廣，但迄今為止還沒有直立穗型秈稻品種在生產(chǎn)上有應(yīng)用。兩個(gè)秈型直立穗突變體ep2-1 和ep2-2，都是自然突變且等位。通過圖位克隆的策略克隆了EP2，并且轉(zhuǎn)基因互補(bǔ)試驗(yàn)恢復(fù)了ep2-1 的表型。與野生型相比，ep2 突變體莖稈粗壯且有更多的維管束，這也解釋了突變體穗直立的表型。EP2 在節(jié)間的維管束特異表達(dá)，編碼一種植物特有的蛋白，該蛋白定位在內(nèi)質(zhì)網(wǎng)，生物學(xué)功能未知。此外，EP2 也調(diào)節(jié)其它的穗性狀，如穗長度和谷粒大小，但每穗粒數(shù)基本沒變化。這些結(jié)果暗示ep2 基因可以應(yīng)用于水稻直立穗的育種中。